At the risk of sounding dreadful, have a question about 'wp'

That sounds like bad advice. Unless the tables are large and badly indexed which I doubt for wp. WP tables are pretty well organised and created efficiently with good design.

Generally, joins are much faster than making separate multiple individual queries. I use joins constantly and they have never been the source of overhead problems or site slowdowns, and I doubt they ever are. The only thing I do now more than before is with multiple joins to make sure I am selecting only the data I need, rather than a blanket fetch all *. Although I have to go back occasionally to add a field I missed, I believe this is probably the best was to control my data sets.

Without joins, I cannot imagine how clunky and loopy my code would have to become.

You will get lots of advice from people, the art is in deciding if it is good advice or not.

Best wishes,

Paul.

PS Perhaps the advice is out of context, although I cannot imagine a context where 'avoid Joins' would make any sense at all.